Calculate your Body Mass Index instantly — find your healthy weight range
BMI, or Body Mass Index, is a screening measure used to categorize adults based on the relationship between their weight and height. It was developed in the 19th century by Belgian mathematician Adolphe Quetelet and is now used worldwide by healthcare professionals as a quick first-step assessment. BMI is calculated as weight in kilograms divided by height in meters squared (kg/m²). The result places a person into one of four standard ranges defined by the World Health Organization: underweight, normal, overweight, or obese. While BMI is widely used because it's simple and inexpensive, it has well-documented limitations — most notably that it doesn't differentiate between muscle and fat mass, which can produce misleading results for athletes, the elderly, or specific ethnicities.
Common contexts: initial screening during medical checkups; population-level health studies and statistics; insurance assessments; eligibility for certain medical procedures or treatments; tracking general trends over time at a population level; nutrition counseling and dietitian consultations; and personal awareness of where you sit relative to standard categories. BMI is meant to be one piece of a larger health picture — typically combined with blood pressure, cholesterol levels, waist circumference, lifestyle factors, and family history.
Underweight: BMI below 18.5
Normal weight: BMI 18.5 to 24.9
Overweight: BMI 25.0 to 29.9
Obese: BMI 30.0 and above
These ranges apply to adults aged 20 and older. Children and teens use age-specific BMI percentiles instead. The categories are population averages — individual health varies widely within and between ranges.
BMI does not measure body fat directly. Two people with the same BMI may have very different body compositions.
BMI does not work well for everyone. Athletes with high muscle mass may register as overweight despite being healthy. Older adults may register as normal weight despite having low muscle mass. People of different ethnicities may have different healthy BMI thresholds.
BMI is not appropriate for pregnant women or children using these adult ranges.
BMI is not a substitute for medical evaluation. Healthcare professionals consider many factors beyond BMI when assessing health.
1. Choose Metric (kg/cm) or Imperial (lb/ft) units
2. Enter your weight and height
3. Click "Calculate BMI"
4. The calculator shows your BMI value, category, and the healthy weight range for your height
5. Remember: this is a screening tool, not a diagnosis
✅ 100% free — no signup, no ads in tool, no tracking
✅ Both Metric and Imperial unit systems
✅ Visual BMI scale with all four WHO categories
✅ Healthy weight range calculated for your height
✅ Client-side only — your measurements never leave your device
✅ Works on Windows, Mac, Linux, Android, iOS — any browser
BMI is calculated as weight in kilograms divided by height in meters squared (BMI = kg/m²). For Imperial units, the formula is (weight in lb × 703) ÷ (height in inches squared). The FileTools BMI Calculator handles both unit systems automatically — just select your preferred system and enter your measurements.
The World Health Organization defines four standard categories for adults: Underweight (BMI below 18.5), Normal weight (18.5 to 24.9), Overweight (25 to 29.9), and Obese (30 and above). These ranges apply to most adults aged 20 and older but may not be appropriate for athletes, pregnant women, the elderly, or children.
BMI is a useful screening tool but has limitations. It does not distinguish between muscle and fat, doesn't account for body composition, age, sex, or ethnicity, and may misclassify athletes (high muscle mass) and elderly adults (lower muscle mass). BMI should be one of several factors a healthcare professional considers — not a definitive measure of health.
BMI is just one number among many health indicators. If you have questions or concerns about your weight or health, please speak with a qualified healthcare professional who can consider your full picture — body composition, lifestyle, medical history, and personal goals. Do not make significant health decisions based on BMI alone.
No. The BMI ranges shown here apply only to adults aged 20 and older. For children and teenagers (ages 2-19), pediatricians use BMI-for-age percentiles that account for growth and development. Consult a healthcare provider for age-appropriate assessment of children and teens.
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